This project seeks to determine how waking neurobehavioral functions (sleep propensity, cognitive performance, sleepiness, and mood) are affected by partial sleep deprivation (PSD). PSD has been identified as a serious public health problem being experienced daily by millions of people as a result of medical, psychiatric, and sleep disorders, as well as social demands (work, family, travel). Although highly prevalent, little scientific work has been done on the nightly duration of sleep and number of days of PSD that will lead to daytime sleepiness, involuntary sleep episodes, performance failures--information that is essential to determining the level of PSD that could result in accidents (e.g., motor vehicle). In a preliminary study, we developed a protocol for studying PSD and demonstrated the sensitivity of a set of neurobehavioral measures to sleep restriction over 1 week. Utilizing this approach, a parametric experiment using independent groups was proposed to test the effects on waking function of the types of sleep restriction most commonly experienced by people. Therefore, the purpose of this study is to determine the nature of the cumulative waking changes in neurobehavioral functions engendered by restricting nocturnal sleep to 4.0 hrs, 6.0 hrs, and 8.0 hrs (control) per night for 14 consecutive nights. Following a 7-14 day period at home, during which time the subjects will be monitored to ensure they have a stable sleep/wake cycle, subjects will live in the Inpatient Study Unit of the CRC for 20 consecutive days, during which time their sleep and waking neurobehavioral functions will be monitored. Following 3 baseline days of 8-10 hr sleep/night, subjects will be randomly assigned to one of three sleep restriction conditions (4,6,8 hr/night) for the next 14 days, followed by 3 days of recovery sleep (8 hr/night).